Joining long lengths MDF with biscuit joins

I've got two long pieces of melamine covered MDF to cover a pipe that runs floor to ceiling in my unit's laundry. It will be an L shaped cover in the corner. I thought I might be able to use concealed biscuit joins to join them together and purchased a joiner, but was a bit annoyed that the biscuits didn't hold the pieces in place - they just slip about. I didn't realise this as I thought they would be tight like tenons and hold the pieces together while the glue dried. So now I'm a bit lost as to what to do. The pieces are 2.4 long by about 500mm wide. I could continue with the biscuits but how on earth to keep the L piece from falling over and tightly engaged while I set it up and the glue dries? I don't have a work bench so am assembling on the floor.

Do you have a picture?

2.4 of chipboard melamine isn't very strong or resistant to bending. Building a frame to attach it too might be better (like a corner kitchen cupboard)

If you are trying to join them like a giant butt joint, then it's normal to use biscuits, screws with little cover caps, glue and clamps, but clamping might be a challenge.

If you know someone with a Festool domino, the littlest dominos would do a very good job.

Send some pix and you will be flooded with ideas.

The biscuits will swell as they absorb moisture from the glue, so they don't have to be a really tight fit in the sockets when dry. If the L shaped part is going into the laundry, and going floor to ceiling, I hope the MDF core is HMR (heat and moisture resistant), as otherwise sooner or later it will absorb moisture from spills or floor washes and swell and ultimately starting disintegrating.

With regard to locking the two pieces together at right angles while the glue dries, I would suggest some screwed angle brackets on the inside surface. If needed these can be removed ion prior to installation, but it would probably pay to leave them if possible.

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Originally Posted by malb

The biscuits will swell as they absorb moisture from the glue, so they don't have to be a really tight fit in the sockets when dry. If the L shaped part is going into the laundry, and going floor to ceiling, I hope the MDF core is HMR (heat and moisture resistant), as otherwise sooner or later it will absorb moisture from spills or floor washes and swell and ultimately starting disintegrating.

With regard to locking the two pieces together at right angles while the glue dries, I would suggest some screwed angle brackets on the inside surface. If needed these can be removed ion prior to installation, but it would probably pay to leave them if possible.

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HMR stands for Highly Moister Resistant, not heat and moister resistant

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Originally Posted by rwbuild

HMR stands for Highly Moister Resistant, not heat and moister resistant

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That's what I had assumed for the last five years, until a few weeks ago when someone that I thought should know better than me told me it was heat and moisture resistant. Have since googled and figure that he talking though his hat, that your interpretation and my original assumption were correct.

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Originally Posted by RussellB

I've got two long pieces of melamine covered MDF to cover a pipe that runs floor to ceiling in my unit's laundry. It will be an L shaped cover in the corner. I thought I might be able to use concealed biscuit joins to join them together and purchased a joiner, but was a bit annoyed that the biscuits didn't hold the pieces in place - they just slip about. I didn't realise this as I thought they would be tight like tenons and hold the pieces together while the glue dried. So now I'm a bit lost as to what to do. The pieces are 2.4 long by about 500mm wide. I could continue with the biscuits but how on earth to keep the L piece from falling over and tightly engaged while I set it up and the glue dries? I don't have a work bench so am assembling on the floor.

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Hi Russell

to answer your question ...
to keep the biscuit jointed butt joint you described together you would use something like a Zeta P2 connector.

the bad news -- as far as I can work out the connectors cost about $2 each and the minimum quantity is 80


Also, if it's in a unit, are you permitted to cover the pipe -- normally pipes like the one you describe are part of the building fabric for insurance and maintenance purposes.

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Originally Posted by RussellB

I've got two long pieces of melamine covered MDF to cover a pipe that runs floor to ceiling in my unit's laundry. It will be an L shaped cover in the corner. I thought I might be able to use concealed biscuit joins to join them together and purchased a joiner, but was a bit annoyed that the biscuits didn't hold the pieces in place - they just slip about. I didn't realise this as I thought they would be tight like tenons and hold the pieces together while the glue dried. So now I'm a bit lost as to what to do. The pieces are 2.4 long by about 500mm wide. I could continue with the biscuits but how on earth to keep the L piece from falling over and tightly engaged while I set it up and the glue dries? I don't have a work bench so am assembling on the floor.

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Personally I would not be using MDF in a laundry, however my suggestion is:-
Champher one side of say 25mm square timber to give you a mounting face for the MDF, mount these full length pieces to the wall each side of the pipe with whatever fittings are suited to the wall material and then attach the MDF across the front so it 'miters' the corner'. Be sure to paint/seal the wall pieces and exposed edges of the MDF first.
Also be sure to seal the join at the floor/wall with No more Gaps etc to prevent water getting under/behind it.
This looks neater and is stronger than the L type cover.

Just my 2/- worth
stay happy